Copyright and fair use laws are kind of screwy, and I don't even pretend to understand them.
In Canada, I took a law class as an undergrad. An interesting example:
Suppose I have an Abba tape which I purchased. (Alright, it's a contrived example)
I loan the tape to my friend Alice. She copies the tape for her own use, and gives me back the original. This is legitimate.
Then I loan the tape to my friend Bob. He copies the tape for his own use, and gives me back the original. This is legal.
So in the end, I have the original, and Alice and Bob have duplicates.
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Suppose a different example. This time I loan the tape to my friend Alice, who makes a duplicate, and gives me back the original. She loans her duplicate to Bob, who then makes a copy and returns the duplicate to Alice.
This is not legal, even though the end result is the same.
So copyright law considers the method of duplication, not just the net effect. (Although whether the second case is ethical is another question - ethical and legal aren't necessarily the same thing)
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To draw an analogue to this current situation, suppose LL finally went ahead and implemented a few more texture layers for avatars. So maybe we could have a tattoo as an under-undershirt. I'm sure we can all agree this would be legitimate, and most welcome.
What Kyrah is proposing to do will achieve the same net result, but through unorthodox means. I have no idea if this is legal or ethical. If I were the skin designer, I wouldn't condone it, but I wouldn't get mad about it either.